Image:Aid agencies helped thousands left homeless after the 2010 earthquake

In a statement, Ms Lawrence said: "Over the last few days we have become aware that concerns were raised about the behaviour of staff in Chad, as well as Haiti, that we failed to adequately act upon.

"It is now clear that these allegations - involving the use of prostitutes and which related to behaviour of both the Country Director and members of his team in Chad - were raised before he moved to Haiti.

"As programme director at the time, I am ashamed that this happened on my watch and I take full responsibility.

"I am desperately sorry for the harm and distress that this has caused to Oxfam's supporters, the wider development sector and most of all the vulnerable people who trusted us."

International Development Secretary Penny Mordaunt said the charity had lied and failed in its "moral leadership" by not fully disclosing details of its investigation to the relevant authorities.

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Video:Oxfam chief: We need to rebuild public trust

She called the behaviour "utterly despicable" and threatened to cut the charity off from Government funding if she was unsatisfied with the answers from Monday's meeting.

The Charity Commission has also said it was not told the full story when Oxfam first looked into the allegations in 2011.

Four members of staff were dismissed and three, including the country director Roland van Hauwermeiren, resigned before the end of the probe.

Following Ms Patel's claims, Downing Street refused to say if the Prime Minister retained full confidence in senior officials at the Department of International Development (DfID).

When asked, a Number 10 spokesman said: "The Prime Minister, of course, has full confidence in the Secretary of State to lead this department, a department which has already taken action on this issue."